Evaluation of the portable Cepheid SmartCycler real-time PCR machine for the rapid diagnosis of foot-and-mouth disease

Direct detection and characterization of foot-and-mouth disease virus in East Africa using a field-ready real-time PCR platform

Effective control and monitoring of foot-and-mouth disease (FMD) relies upon rapid and accurate disease confirmation. Currently, clinical samples are usually tested in reference laboratories using standardized assays recommended by The World Organisation for Animal Health (OIE). However, the requirements for prompt and serotype-specific diagnosis during FMD outbreaks, and the need to establish robust laboratory testing capacity in FMD-endemic countries have motivated the development of simple diagnostic platforms to support local decision-making. Using a portable thermocycler, the T-COR™ 8, this study describes the laboratory and field evaluation of a commercially available, lyophilized pan-serotype-specific real-time RT-PCR (rRT-PCR) assay and a newly available FMD virus (FMDV) typing assay (East Africa-specific for serotypes: O, A, Southern African Territories [SAT] 1 and 2). Analytical sensitivity, diagnostic sensitivity and specificity of the pan-serotype-specific lyophilized assay were comparable to that of an OIE-recommended laboratory-based rRT-PCR (determined using a panel of 57 FMDV-positive samples and six non-FMDV vesicular disease samples for differential diagnosis). The FMDV-typing assay was able to correctly identify the serotype of 33/36 FMDV-positive samples (no cross-reactivity between serotypes was evident). Furthermore, the assays were able to accurately detect and type FMDV RNA in multiple sample types, including epithelial tissue suspensions, serum, oesophageal-pharyngeal (OP) fluid and oral swabs, both with and without the use of nucleic acid extraction. When deployed in laboratory and field settings in Tanzania, Kenya and Ethiopia, both assays reliably detected and serotyped FMDV RNA in samples (n = 144) collected from pre-clinical, clinical and clinically recovered cattle. These data support the use of field-ready rRT-PCR platforms in endemic settings for simple, highly sensitive and rapid detection and/or characterization of FMDV.

Recent advancement in biosensors technology for animal and livestock health management

The term biosensors encompasses devices that have the potential to quantify physiological, immunological and behavioural responses of livestock and multiple animal species. Novel biosensing methodologies offer highly specialised monitoring devices for the specific measurement of individual and multiple parameters covering an animal's physiology as well as monitoring of an animal's environment. These devices are not only highly specific and sensitive for the parameters being analysed, but they are also reliable and easy to use, and can accelerate the monitoring process. Novel biosensors in livestock management provide significant benefits and applications in disease detection and isolation, health monitoring and detection of reproductive cycles, as well as monitoring physiological wellbeing of the animal via analysis of the animal's environment. With the development of integrated systems and the Internet of Things, the continuously monitoring devices are expected to become affordable. The data generated from integrated livestock monitoring is anticipated to assist farmers and the agricultural industry to improve animal productivity in the future. The data is expected to reduce the impact of the livestock industry on the environment, while at the same time driving the new wave towards the improvements of viable farming techniques. This review focusses on the emerging technological advancements in monitoring of livestock health for detailed, precise information on productivity, as well as physiology and well-being. Biosensors will contribute to the 4th revolution in agriculture by incorporating innovative technologies into cost-effective diagnostic methods that can mitigate the potentially catastrophic effects of infectious outbreaks in farmed animals.

Field-Deployable Reverse Transcription-Insulated Isothermal PCR (RT-iiPCR) Assay for Rapid and Sensitive Detection of Foot-and-Mouth Disease Virus

Foot‐and‐mouth disease (FMD) is a highly contagious viral disease of cloven‐hoofed animals, which can decimate the livestock industry and economy of countries previously free of this disease. Rapid detection of foot‐and‐mouth disease virus (FMDV) is critical to containing an FMD outbreak. Availability of a rapid, highly sensitive and specific, yet simple and field‐deployable assay would support local decision‐making during an FMDV outbreak. Here we report validation of a novel reverse transcription‐insulated isothermal PCR (RT‐iiPCR) assay that can be performed on a commercially available, compact and portable POCKIT^™ analyser that automatically analyses data and displays ‘+’ or ‘−’ results. The FMDV RT‐iiPCR assay targets the 3D region of the FMDV genome and was capable of detecting 9 copies of in vitro‐transcribed RNA standard with 95% confidence. It accurately identified 63 FMDV strains belonging to all seven serotypes and showed no cross‐reactivity with viruses causing similar clinical diseases in cloven‐hoofed animals. The assay was able to identify FMDV RNA in multiple sample types including oral, nasal and lesion swabs, epithelial tissue suspensions, vesicular and oral fluid samples, even before the appearance of clinical signs. Clinical sensitivity of the assay was comparable or slightly higher than the laboratory‐based real‐time RT‐PCR assay in use. The assay was able to detect FMDV RNA in vesicular fluid samples without nucleic acid extraction. For RNA extraction from more complex sample types, a commercially available taco^™ mini transportable magnetic bead‐based, automated extraction system was used. This assay provides a potentially useful field‐deployable diagnostic tool for rapid detection of FMDV in an outbreak in FMD‐free countries or for routine diagnostics in endemic countries with less structured laboratory systems.

Preliminary validation of direct detection of foot-and-mouth disease virus within clinical samples using reverse transcription loop-mediated isothermal amplification coupled with a simple lateral flow device for detection

Rapid, field-based diagnostic assays are desirable tools for the control of foot-and-mouth disease (FMD). Current approaches involve either; 1) Detection of FMD virus (FMDV) with immuochromatographic antigen lateral flow devices (LFD), which have relatively low analytical sensitivity, or 2) portable RT-qPCR that has high analytical sensitivity but is expensive. Loop-mediated isothermal amplification (LAMP) may provide a platform upon which to develop field based assays without these drawbacks. The objective of this study was to modify an FMDV-specific reverse transcription–LAMP (RT-LAMP) assay to enable detection of dual-labelled LAMP products with an LFD, and to evaluate simple sample processing protocols without nucleic acid extraction. The limit of detection of this assay was demonstrated to be equivalent to that of a laboratory based real-time RT-qPCR assay and to have a 10,000 fold higher analytical sensitivity than the FMDV-specific antigen LFD currently used in the field. Importantly, this study demonstrated that FMDV RNA could be detected from epithelial suspensions without the need for prior RNA extraction, utilising a rudimentary heat source for amplification. Once optimised, this RT-LAMP-LFD protocol was able to detect multiple serotypes from field epithelial samples, in addition to detecting FMDV in the air surrounding infected cattle, pigs and sheep, including pre-clinical detection. This study describes the development and evaluation of an assay format, which may be used as a future basis for rapid and low cost detection of FMDV. In addition it provides providing “proof of concept” for the future use of LAMP assays to tackle other challenging diagnostic scenarios encompassing veterinary and human health.

Options for decentralized testing of suspected secondary outbreaks of foot-and-mouth disease

This article reviews the options for use of virus detection techniques for decentralized testing of samples from suspected secondary outbreaks of foot-and-mouth disease (FMD). These options have been expanded by the advent of new tests including disposable lateral flow devices (LFDs) that detect viral proteins and portable RT-PCR equipment that detects viral RNA. LFDs have been developed with similar sensitivity to antigen detection ELISA but with the ability to provide a result 1-30 min after the addition of epithelium or vesicular fluid. Portable RT-PCR platforms are being developed that can detect FMD viral RNA in blood, epithelium or other materials with minimal sample processing and with high sensitivity, in as little as 60 min in some cases. These devices may be used on infected farms as pen-side tests, in regional, local or mobile laboratories, or in National Reference Laboratories (NRL). Advantages and disadvantages of different testing options are considered to inform decisions on the optimal strategies for different national circumstances. Issues include validation and quality control, containment needs, availability of test devices and reagents, the decision tree for declaring an outbreak, training issues and provision of samples for subsequent viral characterization. Tests to confirm the diagnosis of the index case of an outbreak of FMD should continue to be carried out in the NRL.

Simple and rapid lateral-flow assay for the detection of foot-and-mouth disease virus

A simple lateral-flow assay (LFA) based on a monoclonal antibody (MAb 70-17) was developed for the detection of foot-and-mouth disease virus (FMDV) under nonlaboratory conditions. The LFA was evaluated with epithelial suspensions (n = 704) prepared from current and historical field samples which had been submitted to the Pirbright Laboratory (United Kingdom) and from negative samples (n = 100) collected from naïve animals in Korea. Four FMDV serotypes (type O, A, Asia 1, and C) were detected in the LFA, but not the remaining three FMDV serotypes (SAT 1, SAT 2, and SAT 3). The diagnostic sensitivity of the LFA for FMDV types O, A, C, and Asia 1 was similar, at approximately 87.3%, to that of 87.7% obtained with antigen enzyme-linked immunosorbent assay (Ag-ELISA). The diagnostic specificity of the LFA was 98.8%, compared to 100% for the Ag-ELISA. These results demonstrate that the LFA using the FMDV MAb 70-17 to detect FMDV is a supportive method for taking rapid measurements at the site of a suspected foot-and-mouth disease outbreak in Asia before diagnosing the disease in the laboratory, thereby offering the possibility of implementing control procedures more rapidly.

Validation of two real-time RT-PCR methods for foot-and-mouth disease diagnosis: RNA-extraction, matrix effect, uncertainty of measurement and precision

Real-time reverse transcription polymerase chain reaction (rRT-PCR) assays are being used routinely for diagnosing foot-and-mouth disease virus (FMDV). Although most laboratories determine analytical and diagnostic sensitivity and specificity, a thorough validation in terms of establishing optimal RNA-extraction conditions, matrix effect, uncertainty of measurement and precision is not performed or reported generally. In this study, different RNA-extraction procedures were compared for two FMDV rRT-PCRs. The NucleoSpin columns available commercially combined high extraction efficiency with ease-of-automation. Furthermore, six different FMDV-negative matrices were spiked with a dilution series of FMDV SAT1 ZIM 25/89. Compared to cell-culture-spiked viral control samples, no matrix effect on the analytical sensitivity was found for blood or foot epithelium. Approximately 1log(10) reduction in detection limit was noted for faecal and tongue epithelium samples, whereas a 3log(10) decrease was observed for spleen samples. By testing the same dilution series in duplicate on 10 different occasions, an estimation of uncertainty of measurement and precision was obtained using blood as matrix. Both rRT-PCRs produced highly precise results emphasising their potential to replace conventional virological methods. The uncertainty measurement, as described in this study, proved to be a useful tool to evaluate the probability of making a wrong decision.

A review of RT-PCR technologies used in veterinary virology and disease control: sensitive and specific diagnosis of five livestock diseases notifiable to the World Organisation for Animal Health

Real-time, reverse transcription polymerase chain reaction (rRT-PCR) has become one of the most widely used methods in the field of molecular diagnostics and research. The potential of this format to provide sensitive, specific and swift detection and quantification of viral RNAs has made it an indispensable tool for state-of-the-art diagnostics of important human and animal viral pathogens. Integration of these assays into automated liquid handling platforms for nucleic acid extraction increases the rate and standardisation of sample throughput and decreases the potential for cross-contamination. The reliability of these assays can be further enhanced by using internal controls to validate test results. Based on these advantageous characteristics, numerous robust rRT-PCRs systems have been developed and validated for important epizootic diseases of livestock. Here, we review the rRT-PCR assays that have been developed for the detection of five RNA viruses that cause diseases that are notifiable to the World Organisation for Animal Health (OIE), namely: foot-and-mouth disease, classical swine fever, bluetongue disease, avian influenza and Newcastle disease. The performance of these tests for viral diagnostics and disease control and prospects for improved strategies in the future are discussed.

Diagnosis of foot-and mouth disease by real time reverse transcription polymerase chain reaction under field conditions in Brazil

BACKGROUND

Foot-and-mouth disease (FMD) is an economically important and highly contagious viral disease that affects cloven-hoofed domestic and wild animals. Virus isolation and enzyme-linked immunosorbent assay (ELISA) are the gold standard tests for diagnosis of FMD. As these methods are time consuming, assays based on viral nucleic acid amplification have been developed.

RESULTS

A previously described real-time reverse transcriptase polymerase chain reaction (RT-PCR) assay with high sensitivity and specificity under laboratorial and experimental conditions was used in the current study. To verify the applicability of this assay under field conditions in Brazil, 460 oral swabs from cattle were collected in areas free of FMD (n = 200) and from areas with outbreaks of FMD (n = 260). Three samples from areas with outbreaks of FMD were positive by real-time RT-PCR, and 2 of those samples were positive by virus isolation and ELISA. Four other samples were considered inconclusive by real-time RT-PCR (threshold cycle [Ct] > 40); whereas all 200 samples from an area free of FMD were real-time RT-PCR negative.

CONCLUSION

real-time RT-PCR is a powerful technique for reliable detection of FMDV in a fraction of the time required for virus isolation and ELISA. However, it is noteworthy that lack of infrastructure in certain areas with high risk of FMD may be a limiting factor for using real-time RT-PCR as a routine diagnostic tool.

Diagnostic specificity of a real-time RT-PCR in cattle for foot-and-mouth disease and swine for foot-and-mouth disease and classical swine fever based on non-invasive specimen collection

Foot-and-mouth disease virus (FMDV) and classical swine fever virus (CSFV) are highly contagious and can cause great economic losses when introduced into disease-free regions. Accurate estimates of diagnostic specificity (Sp) are important when considering the implementation of surveillance for these agents. The purpose of this study was to estimate diagnostic Sp of a real-time reverse-transcriptase PCR assay developed for detection of FMDV in cattle and domestic swine and CSFV in domestic swine based on non-invasive specimen collection. One thousand and eighty-eight range beef cattle were sampled from thirteen geographic locations throughout Texas. One thousand and one hundred market hogs and cull sows were sampled. Results for both FMDV and CSFV were considered positive if amplification occurred at or before 40 PCR cycles, inconclusive between 40 and 45 cycles and negative otherwise. Ten cattle had nonspecific PCR amplifications for FMDV, but none were classified as positive and only one as inconclusive. Specificity (95% confidence interval) was estimated as 100% (99.7, 100). There were 19 nonspecific PCR amplifications for FMDV in sampled swine with 1 classified as positive, 6 as inconclusive, and 12 as negative. Specificity (95% confidence interval) was estimated as 99.9% (99.5, 100). There were 21 nonspecific PCR amplifications for CSFV, and 1 was classified as positive. Specificity (95% confidence interval) was estimated as 99.9% (99.5, 100). These assays have high Sp, but nonspecific PCR amplifications can occur.

Measurement of airborne foot-and-mouth disease virus: preliminary evaluation of two portable air sampling devices

Until now measurement of airborne foot-and-mouth disease virus (FMDV) in the field has not been attempted or been practical; measurements have been restricted to the laboratory and isolation units using instruments developed in the 1960s. However, with the development of air sampling devices for other biological purposes, there is now the possibility that this short-coming can be overcome and as a result earlier detection of virus may be possible in the future. Two recently-introduced commercially-available portable air sampling devices, the BioCapture 650 and the BioBadge 100, have successfully detected airborne virus in three proof-of-concept experiments involving pigs and cattle infected with FMDV. There is an early indication that these devices have potential for use in the field, but for maximum benefit they will need to be combined with a suitable portable analysis instrument. Further evaluation in the laboratory is required before any field measurements are considered.

Detection of biological threat agents by real-time PCR: comparison of assay performance on the R.A.P.I.D., the LightCycler, and the Smart Cycler platforms

BACKGROUND

Rapid detection of biological threat agents is critical for timely therapeutic administration. Fluorogenic PCR provides a rapid, sensitive, and specific tool for molecular identification of these agents. We compared the performance of assays for 7 biological threat agents on the Idaho Technology, Inc. R.A.P.I.D., the Roche LightCycler, and the Cepheid Smart Cycler.

METHODS

Real-time PCR primers and dual-labeled fluorogenic probes were designed to detect Bacillus anthracis, Brucella species, Clostridium botulinum, Coxiella burnetii, Francisella tularensis, Staphylococcus aureus, and Yersinia pestis. DNA amplification assays were optimized by use of Idaho Technology buffers and deoxynucleotide triphosphates supplemented with Invitrogen Platinum Taq DNA polymerase, and were subsequently tested for sensitivity and specificity on the R.A.P.I.D., the LightCycler, and the Smart Cycler.

RESULTS

Limit of detection experiments indicated that assay performance was comparable among the platforms tested. Exclusivity and inclusivity testing with a general bacterial nucleic acid cross-reactivity panel containing 60 DNAs and agent-specific panels containing nearest neighbors for the organisms of interest indicated that all assays were specific for their intended targets.

CONCLUSION

With minor supplementation, such as the addition of Smart Cycler Additive Reagent to the Idaho Technology buffers, assays for DNA templates from biological threat agents demonstrated similar performance, sensitivity, and specificity on all 3 platforms.

Novel reverse transcription loop-mediated isothermal amplification for rapid detection of foot-and-mouth disease virus

Speed is paramount in the diagnosis of foot-and-mouth disease (FMD) and simplicity is required if a test is to be deployed in the field. The development of a one-step, reverse transcription loop-mediated amplification (RT-LAMP) assay enables FMD virus (FMDV) to be detected in under an hour in a single tube without thermal cycling. A fragment of the 3D RNA polymerase gene of the virus is amplified at 65 degrees C in the presence of a primer mixture and both reverse transcriptase and Bst DNA polymerase. Compared with real-time RT-PCR, RT-LAMP was consistently faster, and ten copies of FMDV transcript were detected in twenty-two minutes. Amplification products were detected by visual inspection, agarose gel electrophoresis, or in real-time by the addition of a fluorescent dye. The specificity of the reaction was demonstrated by the absence of amplification of RNA from other viruses that cause vesicular diseases and from that of genetically related picornaviruses. Diagnostic sensitivity was validated by the amplification of reference FMDV strains and archival material from field cases of FMD. In comparison with the performance of the established diagnostic TaqMan assay, RT-LAMP appears to be sensitive, rapid, specific, and cost-effective, with the potential for field deployment and use by developing countries for FMDV surveillance.

Advances in molecular phytodiagnostics - new solutions for old problems

In the last decade, developments in molecular (nucleic acid-based) diagnostic methods have made significant improvements in the detection of plant pathogens. By using methods such as the polymerase chain reaction (PCR), the range of targets that can now be reliably diagnosed has grown to the extent that there are now extremely few, known pathogens that cannot be identified accurately by using laboratory-based diagnostics. However, while the detection of pathogens in individual, infected samples is becoming simpler, there are still many scenarios that present a major challenge to diagnosticians and plant pathologists. Amongst these are the detection of pathogens in soil or viruses in their vectors, high throughput testing and the development of generic methods, that allow samples to be simultaneously screened for large numbers of pathogens. Another major challenge is to develop robust technologies that avoid the reliance on well-equipped central laboratories and making reliable diagnostics available to pathologists in the field or in less-developed countries. In recent years, much of the research carried out on phytodiagnostics has focussed in these areas and as a result many novel, routine diagnostic tests are becoming available. This has been possible due to the introduction of new molecular technologies such real-time PCR and microarrays. These advances have been complemented by the development of new nucleic acid extraction methods, increased automation, reliable internal controls, assay multiplexing and generic amplification methods. With developments in new hardware, field-portable real-time PCR is now also a reality and offers the prospect of ultra-rapid, on-site molecular diagnostics for the first time. In this paper, the development and implementation of new diagnostic methods based upon novel molecular techniques is presented, with specific examples given to demonstrate how these new methods can be used to overcome some long-standing problems.

Studies of quantitative parameters of virus excretion and transmission in pigs and cattle experimentally infected with foot-and-mouth disease virus

Foot-and-mouth disease virus (FMDV) can be spread by a variety of mechanisms and the rate of spread, the incubation period and the severity of disease depend on a multitude of parameters, including the strain of virus, the dose received, the route of introduction, the animal species and the husbandry conditions. More knowledge with regard to these parameters is urgently needed to improve resource-efficient disease control. This report describes detailed studies of FMDV load, excretion and transmission in pigs infected with FMDV O UKG 2001, O TAW 1997 and C Noville virus and in cattle infected with the O UKG 2001 virus to facilitate use of a "FMDV load framework" for the assessment of transmission risks. Virus replicated rapidly in pigs and cattle exposed by direct contact. The mean incubation period was around 3-4 days for cattle-to-cattle and 1-3 days for pig-to-pig transmission, depending on the intensity of contact. The results confirmed that a strong relation exists between dose and length of incubation period. Clinical disease was severe in pigs but relatively mild in inoculated cattle; contact infection of cattle appeared to increase the severity of lesions. FMDV RNA was recovered in nasal and mouth swabs from inoculated animals soon after they developed a viraemia and probably reflected the early production and excretion of virus. FMDV RNA in nasal and mouth swabs from contact animals could be detected several days before they showed other signs of infection, indicating the possibility of detecting exposed animals during the incubation period. FMDV RNA could also be detected in swab samples after the viraemic phase. This may have represented background environmental virus that had been trapped in the respiratory tract and mouth. Alternatively, it may have indicated a somewhat slower clearance or half-life of viral RNA or an extended low level of FMDV replication at these sites. The pattern of FMDV RNA concentrations in pigs was closely similar to that in cattle, but the amounts of FMDV RNA were higher.

Foot-and-mouth disease

Foot-and-mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals. The disease was initially described in the 16th century and was the first animal pathogen identified as a virus. Recent FMD outbreaks in developed countries and their significant economic impact have increased the concern of governments worldwide. This review describes the reemergence of FMD in developed countries that had been disease free for many years and the effect that this has had on disease control strategies. The etiologic agent, FMD virus (FMDV), a member of the Picornaviridae family, is examined in detail at the genetic, structural, and biochemical levels and in terms of its antigenic diversity. The virus replication cycle, including virus-receptor interactions as well as unique aspects of virus translation and shutoff of host macromolecular synthesis, is discussed. This information has been the basis for the development of improved protocols to rapidly identify disease outbreaks, to differentiate vaccinated from infected animals, and to begin to identify and test novel vaccine candidates. Furthermore, this knowledge, coupled with the ability to manipulate FMDV genomes at the molecular level, has provided the framework for examination of disease pathogenesis and the development of a more complete understanding of the virus and host factors involved.

Smallpox and pan-orthopox virus detection by real-time 3'-minor groove binder TaqMan assays on the roche LightCycler and the Cepheid smart Cycler platforms

We designed, optimized, and extensively tested several sensitive and specific real-time PCR assays for rapid detection of both smallpox and pan-orthopox virus DNAs. The assays are based on TaqMan 3'-minor groove binder chemistry and were performed on both the rapid-cycling Roche LightCycler and the Cepheid Smart Cycler platforms. The hemagglutinin (HA) J7R, B9R, and B10R genes were used as targets for the variola virus-specific assays, and the HA and DNA polymerase-E9L genes were used as targets for the pan-orthopox virus assays. The five orthopox virus assays were tested against a panel of orthopox virus DNAs (both genomic and cloned) at the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID). The results indicated that each assay was capable of detecting both the appropriate cloned gene and genomic DNA. The assays showed no cross-reactivity to the 78 DNAs in the USAMRIID bacterial cross-reactivity panel. The limit of detection (LOD) of each assay was determined to be between 12 and 25 copies of target DNA. The assays were also run against a blind panel of DNAs at the Centers for Disease Control and Prevention (CDC) on both the LightCycler and the Smart Cycler. The panel consisted of eight different variola virus isolates, five non-variola virus orthopox virus isolates, two varicella-zoster virus isolates, and one herpes simplex virus isolate. Each sample was tested in triplicate at 2.5 ng, 25 pg, 250 fg, and 2.5 fg, which represent 1.24 x 10(7), 1.24 x 10(5), 1.24 x 10(3), and 1.24 x 10(1) genome equivalents, respectively. The results indicated that each of the five assays was 100% specific (no false positives) when tested against both the USAMRIID panels and the CDC blind panel. With the CDC blind panel, the LightCycler was capable of detecting 96.2% of the orthopox virus DNAs and 93.8% of the variola virus DNAs. The Smart Cycler was capable of detecting 92.3% of the orthopox virus DNAs and between 75 and 93.8% of the variola virus DNAs. However, all five assays had nearly 100% sensitivity on both machines with samples above the LOD (>12 gene copies). These real-time PCR assays represent a battery of tests to screen for and confirm the presence of variola virus DNA. The early detection of a smallpox outbreak is crucial whether the incident is an act of bioterrorism or an accidental occurrence.

Validation of a LightCycler-based reverse transcription polymerase chain reaction for the detection of foot-and-mouth disease virus

A specific reverse transcription polymerase chain reaction (RT-PCR) for the detection of the polymerase gene (3D) of foot-and-mouth disease virus (FMDV) was developed and validated with an analytical sensitivity of equal to, to 1,000 times higher than that of a single passage virus isolation. The performance of the RT-PCR was determined in 180 runs. After implementation, 5.3% of the tests had to be rejected due to invalid controls (e.g. cross-contamination of negative controls). The diagnostic sensitivity, determined using 124 samples from experimentally infected animals, was 91.9% for RT-PCR and 84.7% for virus isolation. Diagnostic specificity, determined by testing 258 samples from uninfected animals, was 100% by both tests. Of the 627 samples tested by RT-PCR and virus isolation, 85 reacted positively in both tests (13.5%) and 447 negatively in both tests (71.3%). One sample was positive by virus isolation and negative by RT-PCR (0.2%), 94 samples were positive by RT-PCR and negative by virus isolation (15%). The majority (84 of 94) of the 15% RT-PCR positive and virus isolation negative samples were among other samples from farms that reacted positively by both tests. The new RT-PCR is a robust, reliable and sensitive test, provided that adequate measures are taken to prevent cross-contamination. A possible preventive measure is to exclude ELISA positive samples from the RT-PCR testing.

The pathogenesis and diagnosis of foot-and-mouth disease

The pathogenesis of foot-and-mouth disease (FMD) is reviewed, taking account of knowledge gained from field and experimental studies and embracing investigations at the level of the virus, the cell, the organ, the whole animal and the herd or flock. The review also addresses the immune response and the carrier state in FMD. Progress made in understanding the pathogenesis of the disease is highlighted in relation to developments in diagnosis and methods of control.